System for picture transmission



April 29, 1930. KAGELMANN ET AL SYSTEM FOR PICTURE'TRANSMISSION Filed April' 13, 1928 Y (14 G Eulenhbf r Patented Apr. 29, 1930 UNITED STATES" PATENT OFFICE MAX KAGELMANN, OF BERLIN-NIEDERSCHONHAUSEN, AND ADOLF EIILENHfiFEB, OF KONIGWUSTERHAUSEN, NEAR BERLIN, GERMANY, ASSIGNORS To C. LORENZ .AKTIENGESELLSCHAFT, 0F BERLIN-TEMPELHOF, GERMANY SYSTEM FOR PICTURE TRANSMISSION Application filed April 1, 1928, Serial No.

The present invention relates to systems for the telegraphic transmission of pictures, documents, writings, and the like, employing synchronously operated members at the transmitting and the receiving stations.

The object of this invention is to provide means for keeping the transmitting and receiving apparatus in exact synchronism.

Another object of the invention is to produce synchronizing electric current impulses at the transmitting station and to send them to the receiving apparatus, to control the synchronous operation thereof.

A further object of the invention is to provide means which enable the synchronizing current impulses to be produced by the transmit-ting apparatus and to be sent to the re ceiving station across the same transmitting channel as that used for the transmission of the picture signals without interference between the picture signals and the synchronizing current impulses.

Still a further object of the invention is to provide means at the receiving station adapted for the separation of the picture signals from the synchronizing signals transmitted by the same channel and to apply them to their respective functions.

The invention is furthermore intended to overcome the disadvantages of the system of synchronizing picture transmission apparatus hitherto employed in which the transmission of the picture signals is stopped periodically for a short time, c. g., at the end of each revolution of a revolving transmitting cylinder. During this short interval of time, a special current impulse is transmitted to. the receiving apparatus in order to control its synchronism. These synchronizing intervals will have more or less marked effect on the clearness of reproduction.

A preferred embodiment of this invention has been represented in the appended draw-' ings and is more fully set forth in the following detailed description taken with reference to the same.

In the drawings, Fig. 1 represents a diagram showing picture signals and synchronizing signals superimposed upon each other, just as they appear in the common transmisaeavas, and in Germany Apr1l28, 1927.

sion channel, e. g., an electric transmission line, and

Fig. 2 shows schematically a diagram for a transmitting station and a receiving station of a picture transmission system in accordance with the present invention.

According to this invention, picture signals and synchronizing current impulses having a comparatively larger intensity are sent simultaneously to the receiving station across the same transmitting channel and are separated there by means of a suitable device.

Referring to Fig. 1 of the drawing, a diagram is shown comprising telegraphic picture signals b and synchronizing current impulses 8 simultaneously transmitted and occurring at equal time intervals p and having a larger intensity than the picture signals. The diagram shows the strength of the current as a function of time in case the transmission is effected across a transmission line. In case of a wireless transmission, a carrier'wave will have to be modulated at the transmitting station in accordance with the picture signal and the synchronizing sig nals as shown by" the Fig. 1, and demodulated again at the receiving station, as is well known in the art.

Referring to Fig. 2, which shows schematically the transmitting and receiving parts of a system in accordance with this invention, numeral 1 represents the transmitting cylinder of a well known picture transmission apparatus, e. g., of the telegraphic or an equivalent type. Numeral 2 is a rotating interrupter (commutator) operated at a speed proportional to the speed of the transmitting cylinder for producing the synchronizing current impulses, and 3 is a battery. All of these three elements are connected in parallel between the filament and grid of an electron tube 7, each one in series with a resistance (4, 5, and Grespectively). Numeral 8 is a high-tension battery supplying the anode voltage for the tube 7 By a suitable adjustment of the individual resistances 4, 5, and 6 in series with which there may be, furthermore, biasing batteries, it is possible to obtain in the anode circuit of the tube picture signals and synchronizing signals of tion. In the example shown a transmitting channel 17 is connected to the terminals 9, via a suitable am lifier, relay, or modulator 18 such as may e used for wireless transmission. Similarly on the other end of channel 17 there may be a receiving set, demodulator, relay, and amplifiers denoted by 19.

In the simplest embodiment of a system shown in Fig. 2,.the transmissioncylinder 1 may have a transmitting sheet applied on it,

0 which consists of electrically conducting material on which the picture, drawing and'the like is drawn by means of a non-conducting material. The c linder 1 is rotated at a uniform speed an is simultaneously moved lengthwise parallel to its axis so that a stylus sweeping on the cylinder will efiect a spirallike scanning of the picture and will produce shorter or longer impulses of current in the circuit of battery 3 as shown by bin Fig. 1. Thereby corresponding-voltages will be applied to the grid of t e tube 7, which will produce amplified current impulses in the anode circuit. The rotating interrupter or commutator 2 periodically places the resistance 5 in parallel with the resistance'4, so that synchronizing impulses 8 (see Fig. 1) will be produced having a frequency which is g l'pportional to the speed of the cylinder 1.

e synchronizing impulses will be either superimposed upon the picture signals as seen at c of Fig. 1, or they will occur during the intervals between the same as shown at d of Fig. 1.

It should be understood that according to this invention, further signals having different frequencies and amplitude may be transmitted by the use of further commutators in series with a resistance placed be tween the filament and grid of the tube. These further signals may serve to produce a further efi'ect at the receiving station, e. g., they may be used for starting and stopping the receiving cylinder which runs synchronously with the transmitting cylinder. Practically, the simultaneous production of different current impressions is made possible by the fact that in the grid circuit of the vacuum tube noperceptible current is flowing, in the case of a correct biasing voltage, so that a pure control without any consumption of energy takes place. This constitutes, therefore, an essential improvement over the old telegraphic methodaccording to which picture signals and synchronizing signals are sent directly into the transmission line 17.

Referring to receivinfipart of Fig. 2,the picture signals and sync ronizing signals arriving at the receiving station are applied to the input terminals 10 of a vacuum tube 11 yiathe demodulator or relay, etc.,'19. The

normal current of the tube is given a suitable value, for instance, zero value. The received Every time .a picture signal arrives the string or reed is moved away from the slot,

allowing the registration paper to be influenced by thebeam of light for a shorter or longer time according to the duration of the signal received. Thus, the whole picture, drawing, or any other image, is built u successively. This method is especiall a apted for the transmission ofso-called lack and white pictures, as may be readily seen from the above. In case the picture signals 1) and synchronizing'signa'ls s coincide, as shown at 07in Fig. 1, this will notafl'ect the impression made on the receiving paper, as in this case the string or reed of the galvanometer will only be moved further away from the slot on account of the greater current strength, which hail no influence onthe recording beam of Furthermore, where only a synchronizing impulse is present, such as at d according to Fig. 1. these impulses will produce a mark on the registration paper in the shape of a thin line. It is, therefore, essential in accordance with this invention, to make the frequency of the synchronizing current impulses so low, and the duration of the synchronizing impulses so small, that the impressions roduced on the blank parts of the picture by .t ese synchronizing impulses alone will have no disturbing influence. As experiments have shown, this may be practically obtained without any great difliculty.

The synchronizing signals 8 which are to be used for the control of the synchronism ofthe receiving cylinder are separated from the picture signals 3 by means of a device which will respond only to currents of higher intensity corresponding to that of the synchronizing signals. In the example shown, an electron tube 13 is provided for this purpose.

The operation of this tube is so adjusted that only the stronger synchronizing currents will produce a sufiicient voltage drop in a resistance 14: placed between grid and filament of 'tube 13 and inserted in the anode circuit of tube 11. This voltage drop is large enough to produce corresponding current variations in the anode circuit of the tube 13. For this purpose, the grid of tube 13 may be given a suitable biasing potential. Thus. the weaker picture signals will not be transferred to the anode circuit of tube 13 which carries only the synchronizing impulses. T hesc are taken off at the terminals 16 and are used to control the synchronization of a device driving the receiving cylinder. Experiments made with respect to the separation of picture signals and synchronizing signals, as described, have shown that a ratio of 1 G of picture signal intensity to synchronizing signal intensity produces good practical results. Numeral 15 is an anode battery'for tube 13. Tube 11 is supplied by a separate battery 15'. The synchronizing signals supplied at the terminals 16 may serve, for instance, to control a synchronous motor driving the receiving cylinder or they may be used to operate a phonic wheel which is intended to control the synchronism in a manner well known in the art.

The synchronizing signals when produced in the above manner have a more or less rectangular shape and according to this invention, a harmonic frequency of the synchronizing signal frequency may be used for the control of synchronism. This harmonic frequency is segregated by known means such as by a filter circuit and is amplified to a suitable degree necessary for the control. This permits the use of a verv low frequency for synchronizing impulses, thereby reducing the disturbing influence on the received picture, as described above.

Having described our invention, what we believe to be new and desire to secure and protect by Letters Patent of the United States is 1. A picture transmission system comprising, in combination, a transmitting apparatus for scanning the picture to be transmitted and producing picture currents corresponding to the individual picture elements, means associated with said transmitting apparatus for producing synchronizing currentimpulses superimposed upon said picture currents and being of a difierent intensity from said picture currents, a transmission channel for sending said picture currents and said synchronizing currents simultaneously to a receiving station. receiving apparatus for reconstructing the picture operated synchronously with said transmitting apparatus by said synchronizing currents, and means at aid receiving station responsive only to currents of distinct intensity, for separating said synchronizing currents rom said picture currents.

2. A picture transmission system comprising, in combination, a transmitting apparatus for scanning the picture to be transmitted and producing electric currents corresponding to the individual picture elements, a vacuum tube having a cathode, a grid, and an anode, a resistance placed between said cathode and said grid, connections to this resistance from said transmitting apparatus to produce corresponding grid potential variations of said vacuum tube, a further resist ance placed between said cathode and said grid in series with a circuit interrupting deand said synchronlzing currents to a receiving station, a receiving apparatus operated synchronously with said transmitting apparatus by said synchronizing currents, and adapted for transforming said picture currents into individual picture elements, and means responsive only to currents of a distinct strength for segregating said synchronizing currents from said picture currents.

3. A picture transmission system comprising, in combination, a rotating cylinder simultaneously moved lengthwise with respect to its axis and being of conducting material, the picture to be transmitted being applied on said cylinder by means of a non-conducting material, a stylus sweeping 'on said cylinder in a spiral-like manner, and adapted to produce impulses of current in an electrical circuit of shorter or longer duration according to the individual picture elements, a vacuum tube having a cathode, a grid, and an anode, a resistance placed between said cathode and said grid, connections to this resistance from said transmitting apparatus to produce corresponding grid potential variations of said Vacuum tube, a. further resistance placed between said cathode and said grid in series with a circuit interrupting device operated in synchronism with said transmitting apparatus, said resistances being sochosen that by the action of said interrupting device periodically connecting and disconnecting said further resistance, synchronizing current impulses of greater intensity than that of said picture currents will be produced in the anode circuit of said vacuum tube, an electric transmission cliannel connected to the anode circuit of said vacuum tube for simultaneously sending said picture currents and said synchronizing currents to a receiving station, a receiving apparatus synchronously operated with said transmitting apparatus by said synchronizing currents, and adapted for transforming said picture currents into individual picture elements, and means responsive only to currents of a distinct strength for g the same nature for segregating said synchronizing currents from said picture currents.

4. A picture transmission system as in claim 3, in which the means for segregating said synchronizing currents from said icture currents comprise a vacuum tube, iaving cathode, grid and anode, a resistance placed between said cathode and said grid, and inserted in a circuit carrying said synchronizing and said picture currents, said resistance being so chosen that onl the stronger synchronizing currents pro uce a voltage drop large enough to cause correspondmg variations in the anode circuit of said tube.

5. A picture transmission system comprising means for producing direct current impulses corresponding to picture elements, means for superposin other direct current impulses overlapping the picture current and of difi'erent intensity for synchronizing purposes, and means for segregating said current impulses to utilize them for their respective functions.

6. In a picture transmission system, means for producing unilateral current impulses characteristic of picture elements, a discharge valve with a control electrode, connections to said control electrode to apply to it said current impulses, means for introducing other overlapping current impulses of the same nature but different magnitude at periodic intervals to said control electrode for synchronizing purposes, and an output circuit to a transmitting channel from said discharge valve to communicate superimposed picture element impulses and synchronizing impulses.

7. In a picture transmission system, means for producing unilateral current impulses characteristic of picture elements, other means for superimposing other overlapping current impulses of greater magnitude but synchronizing purposes, a transmitting channel for said superimposed impulses, a receiving circuit for said impulses comprising a discharge valve with a control electrode, connections to said control electrode from said transmitting channel for receiving said impulses, a device associated with said circuit responsive to all impulsescbelow a certain magnitude to record the picture current impulses for reproducing the picture, means to make said valve responsive to impulses in excess of picture element impulses only, and an output circuit for said discharge valve to apply said synchronizing impulses to their proper function.

8. A picture transmission system having synchronously operated transmitting and receiving devices, comprising in combination, a transmitting apparatus for scanning the picture to be transmitted for producing picture currents, means to produce periodic synchronizing impulses of similar nature and having the same zero amplitude base and means to superimpose both of said impulses for transmission on a common channel.

9. A picture transmission system having synchronously operated transmitting and receiving devices, comprising in combination, a transmitting apparatus for scanning the picture to be transmitted for producing picture currents, means to )roduce periodic synchronizing impulses 0 similar nature and having the same zero amplitude base, means to superimpose both of said impulses for transmission on a common channel a common receiving circuit for both of said impulses, a receiving device in said receiving circuit, being non-responsive to currents in excess of said picture current impulses for receiving said picture currents and recording the picture, and a further receiving device in said receiving circuit responsive only to currents in excess of said picture current impulses for segregating said synchronizin impulses for controlling the synchronism 01 the receiving device in respect to said transmitting apparatus.

10. .In a picture transmission system in accordance with claim 8, means for superimposing said picture current impulses and said synchronizing current impulses, said means comprising a discharge tube having main electrodes and a control electrode and means including circuit connections for operating said control electrode in accordance with said picture currents and independently in accordance with the synchronizing currents.

11. In a picture transmission system in accordance with claim 8, means for superimposing said picture current impulses and said synchronizing current impulses, said means comprising a discharge tube having main electrodes and a control electrode, means including circuit connections for operating said control electrode in accordance with said picture currents and independently in accordance with the synchronizing currents, circuit branches associated with said control electrode each containing in series a resistance and respectively a biasing battery and an interrupting device operated synchronously with the scanning apparatus of said transmitting apparatus.

12. In a picture transmission system in accordance with claim 9, in which said device ceiving circuits in excxess of said picture current impulses.

13. In a system for transmitting pictures,

using synchronously operated transmitting and receiving devices, the method of transmitting picture current impulses and synchronizing current impulses through a common channel WhlCh comprlses superimpos ng unilateral picture current impulses and synchronizing current impulses overlapping the picture current and of diflr'erent relative intensity than the picture currents and separating both the synchronizing andpicture impulses.

14." In a signalling system, the method of v transmitting at least two difierent signals on arommon channel which consists in usingsu erimposed unilateral current impulses of K di erent intensity and overlapping each other other. I t

15. In a signalling system, the method of transmitting at least two different signals on "a common channel which consists in using sugerimposed unilateral current impulses of di erent intensity and overlapping each other andin utilizing the difierence of intensity for operating marginal devices for se arating the signals.

' testimony whereof we have aflixed our signatures. I

MAX KAGELMANN. I ADOLF EULENHOFER. 

